Emerald Fennell and Sacha Baron Cohen were among the winners at the 73rd annual Writers Guild Awards.
In a major boost ahead of next month's Oscars, Fennell won the best original screenplay prize for her directorial debut Promising Young Woman.
She beat Aaron Sorkin, writer of The Trial Of The Chicago 7 and perhaps her chief rival for the equivalent category at the Academy Awards.
Baron Cohen and his writing team won the Writers Guild's best adapted screenplay award for Borat Subsequent Moviefilm and are also Oscar nominated.
Accepting her prize with a video message from the UK, Fennell, 35, said the win was an "incredible, unbelievable, wonderful, unexpected dream come true".
In his acceptance speech, Baron Cohen nodded to the long list of writers on his headline-making Borat sequel and joked: "I can't help thinking that we won it because 60% of the Writers Guild worked on this thing."
In the TV categories, writers of The Crown Peter Morgan and Jonathan Wilson won the best drama series award while the comedy prize went to the team behind Apple TV+ comedy Ted Lasso, which also won best new series.
The Writers Guild Awards are usually held with concurrent ceremonies on the east and west coasts of the US, but due to the pandemic the 2021 running was a single, pre-recorded show hosted by actor Kal Penn.
The theme of the night was unity, following a tumultuous 12 months in Hollywood.
The 26 awards given out included a best adapted long form prize for the writers of Netflix's chess smash hit The Queen's Gambit while original longform was won by the team responsible for historical drama Mrs America.
Outstanding achievement in episodic comedy went to Tony McNamara for The Great while the drama equivalent was won by Miki Johnson for her work on the Fire Pink episode of Ozark.
Documentary screenplay went to Mark Monroe and Bryan Fogel for The Dissident, which explored the murder of Washington Post journalist Jamal Khashoggi.
As well as her screenplay nomination at the Oscars, Fennell is also up for best director for revenge thriller Promising Young Woman, which is nominated for best picture.
Baron Cohen is nominated for best supporting actor for playing a civil rights activist in The Trial Of The Chicago 7.
Last year the Writers Guild honoured dark comedy Parasite with its best original screenplay prize, while JoJo Rabbit won in the adapted category. Both went on to Oscars success.
The 93rd Academy Awards will take place on April 25.